The present invention relates generally to ultrasonic imaging catheters, and more particularly, to catheters having improved electrical connections for ultrasonic transducers.
Intravascular imaging of blood vessels and surrounding tissues continues to be of great benefit in a wide range of medical fields. A particularly successful design for an intravascular imaging catheter employs a rotatable imaging assembly containing an ultrasonic transducer, where the assembly is attached to the distal end of a flexible drive cable. The transducer may be rotated within a catheter body or sheath in order to transmit an ultrasonic signal and produce a video image by well-known techniques. The transducer element or elements are connected to electronics, typically maintained outside the patient""s body, to produce the video image.
To connect the transducer to the electronics, an electrode or lead typically is physically attached to either the transducer face, or to the face of a matching layer which is, in turn, attached to the transducer face. However, such an attachment (e.g., a soldered silver attachment point) can adversely affect the transmission and receipt of ultrasonic signals by the transducer. In short, the attachment interferes with or blocks at least part of the transmitted and/or reflected signals. This problem is further exacerbated by the fact that such attachments often are made by hand. Attachments made by hand typically vary in both size and location from catheter to catheter. As a result, it can be difficult to predict the amount of interference the attachment will produce for a particular imaging catheter.
The placement and attachment of the transducer onto the imaging assembly likewise presents difficulties. For example, it often is desirable to attach the transducer element to the imaging assembly so that the element is positioned at a certain angle, or a desired offset, with respect to the assembly centerline. For transducers that are placed and affixed by hand, the angle and offset can vary between otherwise identical catheters.
The present invention provides off-aperture electrical connections for ultrasound transducers, imaging assemblies and catheters employing such connections, and methods for their use. The electrical connections of the present invention are intended to overcome at least some of the problems of the prior art. For example, connections of the present invention move the electrode or front lead attachment off-aperture, or off the transducer face. This reduces or eliminates the interference such attachment points may cause to the ultrasound signals transmitted from and/or received by the transducer element. Further, imaging assemblies of the present invention are designed to reduce or eliminate the catheter-to-catheter variations in the transducer""s offset and angular position with respect to the assembly housing centerline. Such assemblies are hence more uniform and predictable.
In one embodiment, the present invention provides a transducer connection apparatus. The connection apparatus includes a washer having a hole therethrough and a transducer element that is at least partially disposed within the washer hole. A matching layer is operably attached to the washer and to the transducer element such that an electrical connection is provided between the washer and the transducer element. In this manner, signals can be sent from, and received by, the transducer by establishing an electrical connection with the washer. For example, in one aspect, a lead is operably attached to the washer. Preferably, this lead also is attached to an electrical signal source to send electrical signals to the transducer element for ultrasound imaging. The electrical connection is made with a reduced concern as to the size or precise location of the attachment point because the lead or other electrical connection device is attached to the washer and not to the transducer or matching layer face.
In one aspect, the matching layer includes a material having an acoustic impedance that is lower than an impedance of the transducer element. Such a matching layer is particularly useful since transducer elements typically have a significantly higher impedance than an impedance of the surrounding tissue being imaged.
In another aspect, at least a portion of the matching layer includes an electrically conductive material. In this manner, the matching layer helps facilitate an electrical connection between the transducer element and the washer. In one aspect, the transducer connection apparatus matching layer has first and second matching layer surfaces defining a thickness therebetween. The second matching layer surface is operably attached to the washer and to the transducer element. In one aspect, the second matching layer surface incudes an electrically conductive material. Preferably, the second matching layer surface is operably attached to the washer using an electrically conductive adhesive material. Alternatively, the second matching layer surface is operably attached to the washer using an electrically non-conductive adhesive material, an ultrasonic or thermal bond, or the like.
In one aspect, the washer includes a flexible circuit, such as a polyimide having at least one electrode. The electrode may be a gold-plated electrode pattern, a copper electrode pattern, or the like. Preferably, at least a portion of the washer comprises an electrically conductive material.
In another aspect, the washer has first and second washer surfaces, an outer diameter and an inner diameter. The washer outer diameter preferably is greater than a matching layer diameter. In this manner, the matching layer and washer can be operably attached to one another, while leaving a portion of the washer exposed to permit a lead or electrode to be attached thereto. The washer and matching layer also may have an elliptical or oval shape. In such a case, the washer has an outer major axis and an inner major axis, with the washer outer major axis being greater than a matching layer major axis. In one aspect, the first washer surface comprises an electrically conductive material and is operably attached to the matching layer. In another aspect, a lead is operably attached to the first washer surface.
In one particular aspect, the transducer element has an outer diameter or major axis that is about equal to the washer""s inner diameter or inner major axis, respectively. In this manner, the transducer element is disposed within the washer hole so that the transducer element is in communication with an inner edge of the washer. The transducer element may be operably attached to the washer inner edge using an electrically conductive epoxy or the like. Alternatively, the transducer element may have an outer diameter or major axis that is less than the washer inner diameter or inner major axis. This configuration creates a gap between the transducer element and the washer""s inner edge when the transducer element is disposed within the washer hole.
In one aspect, the transducer element, washer and matching layer are all generally disk-shaped, although other shapes are possible within the scope of the present invention. Similarly, the matching layer preferably has a diameter or major axis that is greater than the transducer element""s diameter or major axis. Such a relationship facilitates electrical connections between the transducer element and matching layer, and between the matching layer and washer. In one aspect, the washer has a thickness that is greater than the transducer element""s thickness. In this manner, the transducer element may be completely disposed within the washer hole.
In one particular embodiment, a transducer connection apparatus, ostensibly as previously described, further includes a bond layer operably attached to the transducer element. In one aspect, the bond layer is at least partially disposed within the washer hole. The matching layer is operably attached to the washer and bond layer such that an electrical connection is established between the washer and the transducer element. In this manner, the bond layer acts as a second matching layer for the transducer element. In one particular aspect of the embodiment, the bond layer includes an electrically conductive adhesive material for bonding the transducer element and washer to the matching layer. Alternatively, the bond layer comprises an electrically non-conductive adhesive material for bonding the transducer element and washer to the matching layer. In one aspect, the non-conductive bond layer further includes an electrode operably attached to the transducer element and washer.
The invention further provides an exemplary imaging assembly, which includes a housing having a distal end, a proximal end and a longitudinal axis. A transducer connection apparatus is operably attached to the housing. The connection apparatus includes a washer having a hole therethrough and a transducer element that is at least partially disposed within the washer hole. A matching layer is operably attached to the washer and to the transducer element such that an electrical connection is provided between the transducer element and washer.
In one aspect, the imaging assembly further includes a lead operably attached to the washer. In another aspect, the housing and lead are adapted to be attached to a cable. Preferably, the housing and lead are adapted to be attached to an integrated coaxial/drive cable.
In one particular aspect, a portion of the housing forms a generally flat surface to which the connection apparatus is operably attached. In one aspect, the surface is positioned generally parallel to the housing longitudinal axis. Alternatively, the surface is positioned to form a desired angle with the housing longitudinal axis, preferably, an angle that is between about xe2x88x9260 degrees and about +60 degrees, and more preferably, between about xe2x88x9215 degrees and about +15 degrees.
In one aspect, the housing preferably is formed with a throughhole. The washer is operably attached to the surface to at least partially cover a first opening of the throughhole.
In one aspect, a backing material is provided within the throughhole, preferably, a backing comprising sound-attenuating material. In one aspect, the backing material includes an electrically conductive material, and the transducer element is in electrical communication with the backing. In this manner, a back side electrical connection or negative connection or ground can be formed between the housing and the transducer element. In another aspect, the transducer element is in electrical communication with the housing.
Alternatively, the backing material comprises an electrically non-conductive material. An electrode is provided that is operably attached to the transducer element and the housing. In this manner, the electrode provides a back side electrical connection or negative connection or ground from the transducer element to the housing. In another aspect, the transducer element is fully disposed within the washer hole. In one aspect, the housing includes a cap to enclose a second opening of the throughhole to form an air-filled cavity. In this matter, air operates as the backing material. In another aspect, the assembly further comprises an electrode that is operably attached to the transducer element and to the washer to provide a second electrical connection therebetween.
In one embodiment, an imaging assembly according to the present invention includes a housing having a distal end, a proximal end and a longitudinal axis. The housing is formed with an air-filled cavity. A transducer connection apparatus is operably attached to the housing to at least partially cover an opening of the cavity. The connection apparatus includes a washer having a hole therethrough and a transducer element that is at least partially disposed within the washer hole. A first matching layer is operably attached to the washer and to the transducer element so that an electrical connection is provided between the transducer element and washer.
In one aspect, the transducer element is in electrical communication with the housing. In another aspect, the imaging assembly further includes a second matching layer operably attached between the transducer element and the first matching layer.
The invention further provides an exemplary catheter system which includes a catheter body having a distal end, a proximal end and a working lumen. A cable, preferably an integrated coaxial/drive cable, is disposed within the working lumen and an imaging assembly is operably attached to a distal end of the cable. The imaging assembly includes a housing and a transducer connection apparatus operably attached to the housing. The connection apparatus includes a washer having a hole therethrough, a transducer element that is at least partially disposed within the washer hole, and a matching layer operably attached to the washer. The transducer element is in electrical communication with both the housing and the cable.
The present invention further provides exemplary methods of imaging a body lumen. One such method includes providing a catheter system including a catheter body having a distal end, a proximal end and a working lumen. A drive cable and a transmission line are disposed within the working lumen. A housing as previously described is operably attached to the drive cable. The housing includes a transducer connection apparatus as previously described. The method includes inserting the catheter body into a body lumen, energizing the transducer element, capturing a reflected signal and producing an image of the body lumen based on the reflected signal.